Our objective is to obtain direct evidence for biologically active retinoids specifically associated with early cardiovascular development during quail embryogenesis. Endogenous retinoids present in specific regions will be identified, and the biosynthesis of bioactive retinoids in these regions will be studied in tissues in vitro and in embryos in culture. Identification of retinoids will be by HPLC and HPLC-ELectrospray-Ionization-MS. The purpose of these studies is to characterize and quantitate the endogenous retinoids in the heart-forming regions and to identify the vitamin A active forms specifically associated with cardiogenesis. The study of retinoid metabolism in early development is hampered by the small amount of available biological material. We have identified endogenous retinyl esters, retinol, retinal and retinoic acids in the neurula stage quail embryo, providing direct evidence that the avian embryo has the full capability to generate vitamin A-active forms during the critical early stages of heart formation. The diversity of vitamin A functions is likely explained not only by the differences in the spatio-temporal expression patterns of retinoid receptors and their binding proteins, but also by the ability of the cells to generate specific vitamin A-active forms during a particular developmental time frame. Pilot studies indicate that identification of pg-amounts of retinoids will be possible with the tissue of 50 stage 8 quail embryos. After conditions have been developed for a successful separation, characterization and quantitation of retinoids in a small sample, specific heart-forming and extraembryonic vascular areas will be excised and analyzed individually, in pooled samples. Anterior-posterior and left-right sectioning will be performed and samples analyzed to obtain information on retinoids in respect to axial and symmetry aspects of cardiogenic regions.